The present disclosure relates to a developing device for developing an electrostatic latent image using toner, and to an image forming apparatus including the developing device.
It is possible to make a coil using a flat cable. For example, there is known a toroidal coil, in which a flat cable is wound around a body of a toroidal core disposed on a printed substrate, and both ends of protruding wires of the flat cable are electrically connected to patterns of the printed substrate, so that the wires and the patterns constitute a winding around the body of the toroidal core.
There is an image forming apparatus such as a multifunction peripheral, a copier, a printer, or a facsimile machine, which performs printing using developer containing magnetic carrier and toner. This image forming apparatus consumes the toner as printing proceeds. An amount of the magnetic carrier does not change basically. When a ratio of the toner in the developer (a ratio of the toner to the carrier, toner density) decreases, it is necessary to replenish the toner.
In order to determine whether or not it is necessary to replenish the toner, a toner density sensor for detecting toner density is disposed in the developing device of the image forming apparatus. A coil may be used for this toner density sensor. When the toner is consumed so that the ratio of the magnetic carrier is increased, an inductance value of the coil is increased. An output of the toner density sensor has a value corresponding to the toner density. On the basis of a variation of the inductance value of the coil, the toner density may be measured, and it may be determined whether or not the toner replenishment is necessary. In other words, a variation of an amount of the magnetic carrier in the magnetic path is detected. Thus the toner density in the developer is measured.
In the known technique described above, a flat cable is used for the coil. However, the flat cable that is just stuck to a wall of the developing device does not function as the coil. Accordingly, there is a problem that the coil using a flat cable cannot be used for the developing device.
In addition, in the toner density detection, a variation of an amount of the magnetic carrier in the magnetic path is detected. Therefore it is difficult to use the coil with a fixed core such as a toroidal coil in the known technique described above for detection of the toner density. In addition, the developer must not contact with the toroidal coil or the substrate directly. Accordingly, when the toroidal coil of the known technique described above is disposed in the developing device, the toroidal coil must be disposed outside a container of the developing device. Only a part of the toroidal coil can be adjacent to the developer. A variation of the toner density cannot be detected correctly. The toroidal coil of the known technique described above cannot solve the above-mentioned problem.